diff options
author | Sean Christopherson <seanjc@google.com> | 2024-01-10 02:02:29 +0300 |
---|---|---|
committer | Sean Christopherson <seanjc@google.com> | 2024-01-31 02:28:02 +0300 |
commit | 5728a4a0ea79e2f2e650db4793170900e57359a7 (patch) | |
tree | be26b1ae38ccf138b83bf4a46cffbdf85e8f711e | |
parent | d652981db08fe2db185e00ad9cd41871f49807b0 (diff) | |
download | linux-5728a4a0ea79e2f2e650db4793170900e57359a7.tar.xz |
KVM: x86/pmu: Disallow "fast" RDPMC for architectural Intel PMUs
Inject #GP on RDPMC if the "fast" flag is set for architectural Intel
PMUs, i.e. if the PMU version is non-zero. Per Intel's SDM, and confirmed
on bare metal, the "fast" flag is supported only for non-architectural
PMUs, and is reserved for architectural PMUs.
If the processor does not support architectural performance monitoring
(CPUID.0AH:EAX[7:0]=0), ECX[30:0] specifies the index of the PMC to be
read. Setting ECX[31] selects “fast” read mode if supported. In this mode,
RDPMC returns bits 31:0 of the PMC in EAX while clearing EDX to zero.
If the processor does support architectural performance monitoring
(CPUID.0AH:EAX[7:0] ≠ 0), ECX[31:16] specifies type of PMC while ECX[15:0]
specifies the index of the PMC to be read within that type. The following
PMC types are currently defined:
— General-purpose counters use type 0. The index x (to read IA32_PMCx)
must be less than the value enumerated by CPUID.0AH.EAX[15:8] (thus
ECX[15:8] must be zero).
— Fixed-function counters use type 4000H. The index x (to read
IA32_FIXED_CTRx) can be used if either CPUID.0AH.EDX[4:0] > x or
CPUID.0AH.ECX[x] = 1 (thus ECX[15:5] must be 0).
— Performance metrics use type 2000H. This type can be used only if
IA32_PERF_CAPABILITIES.PERF_METRICS_AVAILABLE[bit 15]=1. For this type,
the index in ECX[15:0] is implementation specific.
Opportunistically WARN if KVM ever actually tries to complete RDPMC for a
non-architectural PMU, and drop the non-existent "support" for fast RDPMC,
as KVM doesn't support such PMUs, i.e. kvm_pmu_rdpmc() should reject the
RDPMC before getting to the Intel code.
Fixes: f5132b01386b ("KVM: Expose a version 2 architectural PMU to a guests")
Fixes: 67f4d4288c35 ("KVM: x86: rdpmc emulation checks the counter incorrectly")
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://lore.kernel.org/r/20240109230250.424295-10-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
-rw-r--r-- | arch/x86/kvm/vmx/pmu_intel.c | 22 |
1 files changed, 18 insertions, 4 deletions
diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c index 03bd188b5754..5a5dfae6055c 100644 --- a/arch/x86/kvm/vmx/pmu_intel.c +++ b/arch/x86/kvm/vmx/pmu_intel.c @@ -27,7 +27,6 @@ * "fast" reads, whereas the "type" is an explicit value. */ #define INTEL_RDPMC_FIXED INTEL_PMC_FIXED_RDPMC_BASE -#define INTEL_RDPMC_FAST BIT(31) #define MSR_PMC_FULL_WIDTH_BIT (MSR_IA32_PMC0 - MSR_IA32_PERFCTR0) @@ -72,10 +71,25 @@ static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu, struct kvm_pmc *counters; unsigned int num_counters; - if (idx & INTEL_RDPMC_FAST) - *mask &= GENMASK_ULL(31, 0); + /* + * The encoding of ECX for RDPMC is different for architectural versus + * non-architecturals PMUs (PMUs with version '0'). For architectural + * PMUs, bits 31:16 specify the PMC type and bits 15:0 specify the PMC + * index. For non-architectural PMUs, bit 31 is a "fast" flag, and + * bits 30:0 specify the PMC index. + * + * Yell and reject attempts to read PMCs for a non-architectural PMU, + * as KVM doesn't support such PMUs. + */ + if (WARN_ON_ONCE(!pmu->version)) + return NULL; - idx &= ~(INTEL_RDPMC_FIXED | INTEL_RDPMC_FAST); + /* + * Fixed PMCs are supported on all architectural PMUs. Note, KVM only + * emulates fixed PMCs for PMU v2+, but the flag itself is still valid, + * i.e. let RDPMC fail due to accessing a non-existent counter. + */ + idx &= ~INTEL_RDPMC_FIXED; if (fixed) { counters = pmu->fixed_counters; num_counters = pmu->nr_arch_fixed_counters; |